This invention relates to a new catalyst composition useful for initiating and promoting polymerization of .alpha.-olefins and to a polymerization process employing such a catalyst composition.
It is well known that olefins such as ethylene, propylene, and 1-butene in the presence of metallic catalysts, particularly the reaction products of organometallic compounds and transition metal compounds can be polymerized to form substantially unbranched polymers of relatively high molecular weight. Typically such polymerizations are carried out at relatively low temperatures and pressures.
Among the methods for producing such linear olefin polymers, some of the most widely utilized are those described by Professor Karl Ziegler in U.S. Pat. No. 3,113,115 and U.S. Pat. No. 3,257,332. In these methods, the catalyst employed is obtained by admixing a compound of a transition metal of Groups 4b, 5b, 6b and 8 of Mendeleev's Periodic Table of Elements with an organometallic compound. Generally, the halides, oxyhalides and alkoxides or esters of titanium, vanadium and zirconium are the most widely used transition metal compounds. Common examples of the organometallic compounds include the hydrides, alkyls and haloalkyls of aluminum, alkylaluminum halides, Grignard reagents, alkali metal aluminum hydrides, alkali metal borohydrides, alkali metal hydrides, alkaline earth metal hydrides and the like. Usually, polymerization is carried out in a reaction medium comprising an inert organic liquid, e.g., an aliphatic hydrocarbon and the aforementioned catalyst. One or more olefins may be brought into contact with the reaction medium in any suitable manner, and a molecular weight regulator, which is normally hydrogen, is usually present in the reaction vessel in order to suppress the formation of undesirably high molecular weight polymers. Such polymerization processes are either carried out at slurry polymerization temperatures (i.e., wherein the resulting polymer is not dissolved in the hydrocarbon reaction medium) or at solution polymerization temperatures (i.e., wherein the temperature is high enough to solubilize the polymer in the reaction medium).
Following polymerization, it is common to remove catalyst residues from the polymer by repeatedly treating the polymer with alcohol or other deactivation agent such as aqueous base. Such catalyst deactivation and/or removal procedures are expensive both in time and material consumed as well as the equipment required to carry out such treatment.
Moreover, most slurry polymerization processes employing the aforementioned known catalyst systems are accompanied by reactor fouling problems. As a result of such reactor fouling, it is necessary to frequently stop the process to clean the polymerization reactor.
Recently, catalysts having higher efficiencies have been disclosed, e.g., U.S. Pat. No. 3,392,159, U.S. Pat. No. 3,737,393, Dutch Patent Application No. 7203108 and West German Patent Application No. 2,231,982. While the increased efficiencies achieved by using these recent catalysts are significant, polyolefin powders produced at slurry polymerization temperatures, e.g., less than 100.degree. C., in the presence of such catalysts often have undesirably low bulk densities (usually less than 10 pounds/cubic foot).
In view of the foregoing problems encountered in the use of conventional Ziegler catalysts, it would be highly desirable to provide a polymerization catalyst which is sufficiently active to eliminate the need for catalyst residue removal and which minimizes reactor fouling problems. In slurry polymerization processes, it would be especially desirable to provide a high efficiency catalyst that will yield a polyolefin powder having increased bulk density.